Andrew Mason, co-founder of Chicago-based daily deals website Groupon, has been replaced as CEO, the company announced today. Executive chairman and co-founder Eric Lefkofsky and vice chairman Ted Leonsis will take the helm while the company searches for a full-time replacement.

In a memo, Mason said he was dismissed for several reasons: "From controversial metrics in our S1 to our material weakness to two quarters of missing our own expectations and a stock price that’s hovering around one quarter of our listing price, the events of the last year and a half speak for themselves. As CEO, I am accountable."

Mason added, "I love Groupon, and I’m terribly proud of what we’ve created. I’m OK with having failed at this part of the journey."

Mason most recently came under fire following Groupon's worse-than-expected fourth quarter earnings report this week. The company posted a loss of $81.1 million and indicated revenue growth was to slow down in the first quarter of this year.

Indeed, Mason had been in the hot seat for some time, as reports surfaced last year that the company was unsatisfied with his leadership and had already started looking for a replacement.

Founded in 2008, Groupon effectively pioneered the popularity of daily-deal sites. The company went public in 2011 with early estimates pegging its value at about $11 billion. But Groupon quickly fell out of favor with customers as well as some merchants, with business owners complaining that the deals are difficult to manage and often don't drive additional profits.

"As a founder, Andrew helped invent the daily deals space, leading Groupon to become one of the fastest-growing companies in history," Lefkofsky said of Mason in the announcement.